This invention relates to a novel photocurable composition, more particularly to a photocurable composition which can be cured by irradiation of light within a short time and is suitable for use as ink, paint, adhesive, surface coating material, plate-making material, sealant, electric insulating material, etc.
In recent years, in connection with conservation of energy or workability, processes to cure resins by irradiation of light are coming to the fore of interest. Among them, the process to photocure an epoxy resin can be widely applied and is important. The processes to be used for photocuring of epoxy resins can be classified into the two types.
One is a composition obtained by modification of an epoxy resin with use of a vinyl group-containing compound such as an acrylic ester having a photopolymerizability, which undergoes photopolymerization through the vinyl group. However, the epoxy resin modified with the vinyl group-containing compound is considerably inferior in the adhesion property and the heat resisting property to an unmodified epoxy resin itself.
The other is a composition obtained by curing the epoxy resin itself by use of a catalyst of a photodecomposable type. An example of the catalyst used therefor is a complex represented by the following formula: ##STR1## (wherein Ar represents an aromatic group such as a phenyl group; X represents an iodine atom, a sulfur atom, a diazo group, or the like; and Y represents BF.sub.4, PF.sub.6, AsF.sub.6, SbF.sub.6 or the like), as disclosed in Macromoleculas, 10, 1307 (1977); Journal of Radiation Curing, 5, 2 (1978); Journal of Polymer Science Polymer Chemistry Edition, 17, 2877 (1979); ditto, 17, 1047 (1979); Journal of Polymer Science Polymer Letters Edition 17, 759 (1979); Specification of Japanese Unexamined Patent Publication (KOKAI) No. 65219/1980; specification of U.S. Pat. No. 4,069,054; specification of British Pat. No. 1,516,511; specification of British Pat. No. 1,518,141; etc.
However, the cured resin products obtained by use of these catalysts, while having good mechanical characteristics and heat resistance, inconveniences are involved such that the characteristics may be deteriorated or corrosion phenomenon may be caused by heating or with lapse of time on account of the catalytic component which is a strong acid and becomes ionic impurity, and at the same time great problems remain with repect to workability and handling.
The present inventors have already proposed a photocurable composition comprising an epoxy resin which is photocurable by use of a catalyst comprising an aluminum compound and an .alpha.-ketosilyl compound (Japanese Unexamined Patent Publication No. 125212/1982). This composition, which can overcome almost the problems as mentioned above, was not satisfactory with respect to curing speed.